Biological molecules PAGs

Question 1

Reducing sugars e.g.

Answer 1

Glucose and fructose

Question 2

Non - reducing sugars e.g.

Answer 2

Sucrose

Question 3

Reducing sugars test (simple)

Answer 3

1) Benedict’s solution (and heat)
2) BS - originally blue
3) Copper ions are reduced
4) Turns brick red

Question 4

Non reducing test (simple)

Answer 4

1) Benedict’s solution and heat (wont get a result)
2) Boil with hydrochloric acid
3) Hydrolyse sucrose to fructose/glucose
4) Do reducing sugars test

Question 5

Benedict’s test detailed

Answer 5

1) using standard/known concentrations of reducing sugar serial dilutions
2) heat with benedict’s solution - same volumes each time
3) use excess to create an unknown concentration
4) should change to green/yellow/orange/brown/red
5) remove precipitate/obtain filtrate
6) place samples in the colorimeter
7) calibrate to zero using water
8) use red/orange filter
9) read the transmission - more transmission means more sugar present
10) using standard known concentrations obtain calibration curve
11) plot transmission against reducing sugar concentration
12) use graph to obtain unknown solution concentrations

Question 6

How do you test for lipids

Answer 6

emulsion test
take a sample and mix thoroughly with ethanol as lipids are not soluble in water
-filter
-pour the solution into water in a clean test tube
-cloudy white emulsion indicates presence of lipids

Question 7

How do you test for proteins

Answer 7

biuret test
-if protein is present changes from light blue to lilac
-detects presence of peptide bonds

Question 8

How do you test for starch

Answer 8

Add iodine
changes to a blue/black colour

Question 9

How could a non-reducing sugar be tested for a reducing sugar

Answer 9

-add hydrochloric acid and boil
-add sodium hydrogen carbonate
-carry out reducing sugar test again